Generally, a semiconductor device is completed by forming various pattern regions, such as a device separation film, an interlayer isolation film, an electric conduction film, a contact, etc. on a surface of a semiconductor substrate. The interlayer isolation film is formed of a silicon oxidation film or a nitride film (SixNy) such as a PSG (Phosphorus Silicon Glass), a BPSG (Boron Phosphorus Silicon Glass), an USG (Undoped Silicon Glass), etc. Here, the nitride film serves as an interlayer isolation film. In addition, the nitride film may be used as an etching stopper film in an etching process, a barrier film for preventing any damage of a lower film in a chemical mechanical polishing (CMP) process, a barrier film in formation of a minute pattern such as a self-aligned contact, or a material film for performing a variety of functions, such as an oxygen diffusion prevention film for preventing any diffusion of oxygen into a semiconductor substrate in a device separation process.
Moreover, in manufacturing a DRAM (Dynamic Random Access Memory) device with a property of data volatility, a metal being a low resistance material is used as material of word and bit lines to comply a minute patterning trend due to a reduced design rule and to further improve read/write rates for data, instead of a conventional tungsten silicide or a doped silicon. To prevent heavy metal contamination and thermal transformation of a metal material, which are caused by such a change, it is subject to a low thermal bundle process. Even in this process, the nitride film is used as a barrier film.
Such a nitride film is generally deposited by a thermal CVD (chemical vapor deposition) process using a CVD apparatus of furnace type or by a PECVD (Plasma enhanced CVD) process using a plasma enhanced CVD apparatus of single chamber type.
At this time, In case of forming the nitride film using the thermal CVD apparatus, there is an advantage in that a loading effect and a surface roughness characteristic are excellent, resulting in a good step coverage, whereas there is a drawback in that a thermal bundle is generated in a wafer due to a long time exposure of the wafer to a high temperature, resulting in a degraded electric characteristic due to a deterioration of an electric characteristic and a metal electrode of a device produced on the wafer.
On the contrary, in case of depositing a nitride film using the plasma enhanced CVD apparatus, there is an advantage in that since the nitride film is formed under a low temperature atmosphere, a generation of the thermal bundle can be minimized, whereas there is a drawback in that it is impossible to deposit the nitride film when a step is formed because a loading effect and a step coverage characteristic are not good, and a quality of the nitride film is degraded compared to the thermal CVD process due to an existence of the plasma.
Meanwhile, in forming a small contact of a large scale ingegration semiconductor device with a pattern size 0.5 μm or less, when a blanket etching process using a plasma, and the like is to be performed after a spacer is deposited, it needs a profile of a nitride film 1 with an upper region of a larger thickness compared to thickness B of the side regions or thickness C of the lower region, as shown in FIG. 1.
In this case, in the prior art, a first nitride film 2a with an entirely uniform thickness as shown in FIG. 2a is deposited using the thermal CVD apparatus having an excellent step coverage. Thereafter, a second thick nitride film 2b is deposited on a surface of the first nitride film 2a as shown in FIG. 2b by moving the wafer into the plasma enhanced CVD apparatus such that a profile is obtained in which a thickness of the upper region of the nitride film is larger compared to that of each of the side regions and the lower region.
Thus, in the prior art, there exists a problem that it has complicated processes because, in order to form the nitride film with a larger thickness at the upper region thereof compared to those of the side regions and under region, the nitride film must be formed with a uniform thickness on the entire surface of the wafer using, as a first CVD apparatus, a thermal CVD apparatus with an excellent step coverage characteristic, and then must be, in a further process, formed with a larger thickness at the upper region using, as a second CVD apparatus, another CVD apparatus (i.e., a plasma enhanced CVD apparatus with a high installation at a top region).
There is another problem that when the wafer, in which a thermal bundle is generated due to the thermal CVD process in high temperature, is moved from the thermal CVD apparatus to the plasma enhanced CVD apparatus, it is contaminated by impurities in air.
Accordingly, in the technical field of the present invention, there is a need for a method for depositing a nitride film with a different thickness for each region thereof in one CVD apparatus while further simplifying the process.